IMO, this is not (economically-speaking) rent-seeking.
Apple has created something that improved the world (that created new wealth) and is charging for it. That’s definitionally not rent-seeking.
Apple indeed created new wealth by developing iOS and the App Store. Then, once they owned the market, they started exploiting it by adding new restrictions. The restrictions had no economic value, they're simply there to allow Apple to extract their unfair share of the value created by others.